Sleep bruxism is generally defined as a diurnal or nocturnal parafunctional activity involving: clenching, grinding and gnashing of the teeth. It has been considered that such sleep bruxism is a causatic factor for tremendous problems in odontology (McNeill, C., DDS (ed.), “Temporomandibular Disorders: Guidelines for Classification, Assessment, and Management,” Chicago: The American Academy of Orofacial Pain, Quintessence Books, pp. 11-18[1993]). Excessive dental attrition can never occur any more in the dietary life of modern people, because tooth contacts of the maxillary and mandibular casts will hardly happen during masticatory (chewing) movement of foods taken by the modern people. On the other hand, it is reported that the sleep bruxism may last for from 20 to 40 minutes, in some cases for 2 hours, during a one-night sleep (Trenouth, M. J., “The relationship between bruxism and temporomandibular joint dysfunction as shown by computer analysis of nocturnal tooth contact patterns,” J. Oral Rehabil., Vol. 6, pp. 81-87[1979]).
It is said that the maximum occlusal force generated by masticatory muscles at the time of the sleep bruxism is significantly greater than the force required to fracture teeth. While neuromuscular mechanism is considered to consciously reduce muscular strength against the load suddenly applied against the teeth in order to prevent disorder in a living body, it does not have a function to unconsciously reduce the force applied to enamel or dentinal matrix. Especially, the forces caused by the sleep bruxism may be considered to be out of control by such neuromuscular mechanism.
It is considered that such sleep bruxism has caused a risk to generate many dental disorders such as tooth abfractions, tooth migration, hyperesthesia, wedge-shaped defect, periodontoclasia, dysfunction of temporomandibular joints, and hypertonic masticatory muscles (Coleman, T. A., DDS, et al., “Cervical dentin hypersensitivity. Part II: Associations with abfractive lesions,” Quintessence Int., Vol. 31, No. 7, pp. 466-473[2000]).
Conventional dental occlusion treatments have been studied mainly on masticatory function for a long time, and the purpose of clinical occlusion treatment has been limited only to recovery of masticatory function. In such normal masticatory function by humans, the load applied to teeth, periodontal tissue, temporomandibular joints and the like is not so large that biomechanical consideration has not been seriously taken in occlusal construction. However, since the bruxism function is a very strong masticatory muscle activity, the load applied to teeth, periodontal tissue, and temporomandibular joints may reach a maximum level. Accordingly, it has been recently proposed that the bruxism takes a very important role of a masticatory organ for releasing emotional stress (Slavicek, R. (ed.), “The function of stress management. In: The Masticatory Organ-Function and Dysfunction,” Klostemeuburg, Gamma Medizinish-wissenschaftliche Fortdungs-AG, pp. 281-291[2002]; Sato, S., et al., “Bruxism as a Stress Management Function of the Masticatory Organ,” Bull. Kanagawa Dent. Coll., Vol. 29, No. 2, September, pp. 101-110[2001]), and it has also been suggested that the conventional dental occlusion treatment system should be fundamentally changed (Sato, S., et al., “The Masticatory Organ, Brain Function, Stress-release, and a Proposal to Add a New Category to the Taxonomy of the Healing Arts: Occlusion Medicine,” Bull. Kanagawa Dent. Coll., Vol. 30, No. 2, September, pp. 117-126[2002]). As just described, although the bruxism has now been recognized as a very important issue in clinical dentistry, little approach has been actually made for it.
Thus, up to now, the bruxism has been studied by means of huge facilities such as a sleeping laboratory, polysomnography, electromyography and the like (Sjöholm, T., et al., “Masseter muscle activity in diagnosed sleep bruxists compared with non-symptomatic controls,” J. Sleep Res., Vol. 4, pp. 48-55[1995]; Lavigne, G. J., et al., “Bruxism,” Principles and Practice of Sleep Medicine, 3rd Edition, Kryger M. H., Roth, T., Dement, W. C., editors, Philadelphia: Saunders, W. B., pp. 773-785[2000]). Although these facilities seem to be important for an academic purpose, they are not suited for an application to the daily and clinical diagnosis of a patient. It has been pointed out that many problems in clinical sites such as tooth abfractions, tooth migration, hyperesthesia, wedge-shaped defect, periodontoclasia, dysfunction of temporomandibular joints, and hypertonic masticatory muscles as well as destruction of prosthetic apparatus after treatment and occlusal disruption are attributed to the sleep bruxism and abnormal occlusal contacts during the sleep bruxism. However, there is no method to adequately measure them.
Occlusal construction will finally be required in clinical dentistry. There has been reported very little actual countermeasure against stress bruxism in the course of said construction. The final purpose of dental medicine is considered to contribute to maintenance of good health of an entire body by taking harsh physical environments into account and completing occlusion in response to them. It has to be admitted that progress is very slow with respect to diagnosis of the bruxism.